Pitcher's Thistle (Cirsium pitcheri)
Pitcher's Thistle grows only on shorelines or sand dunes of the Great Lakes in Michigan, Indiana, Wisconsin and Ontario, Canada. It is restricted to the dunes of Lakes Michigan and Huron and a few dune sites along Lake Superior. Pitcher's Thistle was once found in Illinois on the shore of Lake Michigan, but is now extirpated there. Michigan has more locations for this thistle than any other state.
This shoreline plant requires open, windblown sand dunes or low, open beach ridges. Pitcher's Thistle withstands the desert like environment of Michigan's sand dunes by having a root capable of penetrating more than 6 feet into the sand. The silvery hairs covering the plant aid in water retention and reflect some of the sun's strong rays. On dunes it may be found growing with the glossy-leaved dune grasses, the red fruited Bearberry, the bright yellow orange Puccoon, and the beautiful blue Bellflower.
The Great Lakes dunes, formed principally between 5,000 and 14,000 years ago, are a unique and irreplaceable component of Michigan's natural heritage. In addition to being the only home for Pitcher's Thistle, the Great Lakes dunes are the largest system of freshwater dunes in the world.
Pitcher's Thistle is a handsome, white flowered thistle. The plant's silvery appearance is due to dense, white, woolly hairs covering the bluish-green leaves and stems. It may reach a flowering height of 3.5 feet, although flowering plants as small as 5 inches have been seen. The leaves are up to I foot long and deeply divided into narrow, often spine tipped segments. The prickly flower heads bloom from June to September and are cream-colored or slightly pinkish, with a faint pleasant smell. The plant may be found in two stages: flowering and non flowering. A non flowering or juvenile plant is a rosette or cluster of silvery leaves. Juvenile plants take 2 to 8 years to mature to the flowering stage. After flowering and setting seed, adult plants die.
This silvery thistle can be confused with another common dune plant called Wormwood. Wormwood's leaves are more finely divided and are often purple at their base. Wormwood also lacks spines. Other Michigan thistles have pink to purple flowers, lack the silvery appearance, and are very prickly.
Pitcher's Thistle is found only on the dunes and shoreline of Lakes Michigan, Huron, and Superior. It is threatened by loss of habitat due to increased human activity in shoreline areas. Heavy foot and vehicular traffic in dune areas and along the shoreline represent major threats. Pitcher's Thistle is listed as a "threatened" species by the federal government and the state of Michigan. A permit is required for any project (including research, development, and construction) which may "take" or "harm" threatened or endangered species in Michigan.
In addition to aesthetic, ethical, and ecological reasons for protecting Earth's diverse species, another reason can be offered: self-interest. The natural world is our life support system, providing countless medical, agricultural, and commercial benefits. For example, chemicals from plants are the sole or major ingredient in one quarter of all prescription medications in the United States. Scientists have shown that closely related plants usually have similar chemical compounds. Guayule (pronounced gwhy ool' Iee), a drought tolerant shrub of the American Southwest in the same family as Pitcher's Thistle, is being reviewed as a commercial source of natural rubber and may help limit U.S. dependence on imported natural rubber. If we choose to save wild species now, they may offer opportunities for us in the future. We do know that when a species becomes extinct, a unique set of genetic material whose use presently may be unknown, is lost forever.
To conserve the remaining populations of Pitcher's Thistle, private, corporate, and public landowners and land managers who are likely to have Pitcher's Thistle on their property are being contacted. Landowners have the opportunity to assist in the preservation of this remarkable component of Michigan's natural heritage. Other cooperative conservation efforts initiated by the Natural Heritage Program include:
- protecting habitat within public natural areas and private nature
- completing extensive surveys of known and potential habitat of threatened
plants and animals, and
- developing management plans with public agencies and private developers through statewide permitting and enforcement systems.
- Voluntarily protect coastal dunes and shoreline habitat where this and
other special plants and animals of the Great Lakes live.
- Learn the differences between Pitcher's Thistle and Wormwood.
- Report your observations, including possible new locations of Pitcher's
Thistle, by contacting the Michigan Department of Natural Resources.
- Report destruction of this plant or the habitat in which it occurs by
calling the Report All Poaching (R.A.P.) Hotline at 1 800 292 7800.
- Become involved with a land conservation organization.
- Support the Nongame Wildlife Fund by purchasing a wildlife habitat license plate, or through a direct contribution.
Pitcher's Thistle, also known as Dune Thistle, was named in honor its discoverer, Dr. Zina Pitcher. He was a prominent citizen who helped organize the Historical Society of Michigan and the University of Michigan's medical school. While serving as an army surgeon during the 1820's at Fort Brady, Sault Ste. Marie, Dr. Pitcher found this thistle on the Grand Sable Dunes of Lake Superior. Dr. Pitcher, like many early physicians, was also an accomplished botanist.
Acknowledgements: This information was written by Elaine A Chittenden with assistance from the Natural Heritage Program and Michigan Natural Features Inventory staff.